Fan Yang — Michigan Technological University
Mikhail Ovchinnikov — Pacific Northwest National Laboratory
Raymond A Shaw — Michigan Technological University
Category
High-latitude clouds and aerosols
Description
Height versus radius obtained from the Lagrangian tracks for four long-lifetime ice particles. Ice growth is simulated within a 3-D time-dependent field from a large eddy simulation of a supercooled stratiform cloud. Gray shading indicates the mixed-phase cloud region, and the colorbar represents the vertical velocity (in m/s). Red dots represent the initial seeding locations. Trajectory 1 illustrates quasi-steady growth and trajectories 2-4 illustrate recycled growth.
Ice particles play an important role in precipitation and radiation transfer in stratiform mixed-phase clouds. Lagrangian ice particle tracking in mixed-phase clouds is applied in both a 3-D time-dependent velocity field produced by a large eddy simulation cloud model and a 2-D idealized field. It is found that more than 10% of ice particles have lifetimes longer than 1.5 h, much longer than the large eddy turnover time or the time for a crystal to fall through the depth of a nonturbulent cloud. An analysis of trajectories in a 2-D idealized field shows that there are two types of long-lifetime ice particles: quasi-steady and recycled growth. For quasi-steady growth, ice particles are suspended in the updraft velocity region for a long time. For recycled growth, ice particles are trapped in the large eddy structures, and whether ice particles grow or sublimate depends on the ice relative humidity profile within the boundary layer. Some ice particles can grow after each cycle in the trapping region, until they are too large to be trapped, and thus have long lifetimes. The relative contribution of the recycled ice particles to the cloud mean ice water content depends on both the dynamic and thermodynamic properties of the mixing layer. In particular, the total ice water content of a mixed-phase cloud in a decoupled boundary layer can be much larger than that in a fully coupled boundary layer.
